A. Field of the Invention
The present invention relates to a contact plug structure and method for preparing the same, and more particularly, to a contact plug structure and method for preparing the same using the dual-damascene technique.
B. Description of the Related Art
FIG. 1 is a top view of a checkerboard dynamic random access memory 10 according to the prior art, FIG. 2 is close-up solid view of a portion of the checkerboard dynamic random access memory 10 in the dash-lined region, and FIG. 3 shows the equivalent circuit of a portion of the checkerboard dynamic random access memory 10 in the dash-lined region. A contact plug structure 16 is used to electrically connect the bit line 14 of the checkerboard dynamic random access memory 10 to two doped regions 24 and further to two deep trench capacitors arranged in an S-shape manner, as indicated by the S-shaped solid line. Particularly, the two doped regions 24 are positioned at two sides of a word line 20 in an S-shape manner, and a shallow trench isolation structure 22 is used to electrically isolate the doped region 24, as shown in FIG. 2.
The prior art used a single contact plug structure 16 to electrically connect two doped regions 24 positioned at different sides of the bit line 14, and the contact plug structure possesses a very large volume, extending over two doped regions 24 and one shallow trench isolation structure 22 so as to achieve the electrical connection of two doped regions 24 at different sides of the bit line 14. However, the overlapped area between the contact plug structure 16 and the word line 20 is also very large corresponding to the large volume of the contact plug structure 16. The large overlapped area between the word line 20 and the contact plug structure 16 results in serious bit line coupling (BLC), which is an important issue that researchers developing the advanced dynamic random access memory have worked to solve.